Methods for the contact-free measurement of surfaces, with which methods a sequence of strip patterns which are of the same strip direction and which are formed from a multitude of strips is projected by way of a projection device onto a surface to be measured, are known from the state of the art, wherein a picture of the surface is recorded by each of two cameras during the projecting of each of the strip patterns. Corresponding points in picture planes of the camera are then identified by way of the strip patterns which are projected onto the surface, whereupon spatial coordinates of the surface points on the surface are determined by way of triangulation on the basis of the points identified as being corresponding.
Such methods are known e. g from the documents DE 10 2007 022 361 A1 and DE 10 2006 049 695 A1. A common design of such methods envisages some of the projected strip patterns being phase-shifted strip patterns with a sinusoidal brightness course which permit the assignment of a phase value to each point on the surface, wherein some further ones of the projected strip patterns define a grey code which permits an ambiguity which yet remains after determining the phase values to be resolved.
One difficulty which results with such triangulation methods based on pattern projection lies in a relative large number of patterns having to be projected and according many pictures having to be taken, so that the corresponding or homologous points in the picture planes can be indentified in an unambiguous manner and to an sufficiently accurate extent, which of course cannot be effected in an arbitrarily short time. For this reason, the measuring of surface contours by the methods known from the state of the art demands a relatively long measuring duration. This is disadvantageous in many applications, particularly if moved surfaces are to be measured or of a hand-held device is to be used for this.